This has happened to me 2-3 times on my current XR. After a long ride, I shut my bike off. The clutch lever is within spec's(2-3cm). The next time I jump on the bike(after sitting for a few days), there isn't any play in the clutch lever. After riding the bike around the block, all the adjustment 2-3cm comes back into the lever.

Im not sure what is meant by 2-3cm. The clutch should be adjusted such that disengagement starts at 2-4mm. As the engine gets hot, especially the clutch, that play will be lessened which is the reason for the wheel style on the fly clutch adjusters. Refer to a shop manual for proper adjustment.

Yes, I'm talking about the "clutch play" in the lever. The spec is 1-2cm.
This play goes from 2-3cm(which is where I set mine), to 0cm after sitting for a couple days. Then back to 2-3cm after being ridden.

Probably have grooves worn into the basket fingers, makes the adjustment fiddly, eventually you'll get a honking noise and a grabby clutch. Take it apart and check it out. You can file the grooves down to get some more life or get a Hinson billet basket.